Handle Anthropic usage metadata arrays

[cometto2007]

Summary

Fixes Anthropic OAuth usage polling when /api/oauth/usage includes top-level metadata arrays such as limits.

Root Cause

Anthropic now returns additional top-level fields alongside quota buckets. At least one of those fields, limits, is an array. AnthropicQuotaResponse currently unmarshals the entire response as map[string]*AnthropicQuotaEntry, so any array-valued metadata field fails the whole decode with:

json: cannot unmarshal array into Go value of type api.AnthropicQuotaEntry

That matches the failure reported in #82.

Changes

• Adds a custom UnmarshalJSON for AnthropicQuotaResponse.
• Preserves quota-object values and null inactive buckets.
• Ignores non-object metadata fields such as limits arrays.
• Adds a regression test covering the new response shape.

Validation

• go test ./internal/api -run 'TestAnthropicClient_FetchQuotas'
• Also validated the patch against a live Anthropic OAuth usage response in a temporary container before preparing this PR.

Fixes #82.

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/api/anthropic_types.go	77.77%	2 Missing and 2 partials ⚠️

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